1. Field of the Invention
The present invention relates to a sheet separation device and separation method for separating a sheet from a sheet carrying member such as a transfer drum, and image forming device and image forming method using said sheet separation device. More specifically, the present invention relates to an electrophotographic image forming apparatus and image forming method provided with a duplex printing. function, and a sheet separation device and sheet separation method used in such image forming apparatus, for example, a duplex printer, duplex copier, duplex facsimile machine and the like.
2. Description of the Related Art
Image forming apparatuses of the electrophotographic type provided with a duplex printing function, e.g., duplex printer, duplex copiers, duplex facsimile machines and the like, have been proposed. These apparatuses first transfer a toner image to a first surface (front side) of a sheet as a transfer surface, then fuse said toner image to the sheet via heat or pressure, and thereafter transfer a toner image to a second surface (back side) of said sheet as a transfer surface, then fuse said toner image on the sheet in the same manner as on the first surface (front side), so as to form toner images on both sides of the printed (fixed) sheet.
Color image forming apparatuses of the electrophotographic type provided with a duplex printing function have been proposed. For example, color duplex printer, color duplex copiers, color duplex facsimile machines and the like have been proposed. In these devices, toner images of yellow (Y), magenta (M), cyan (C), and black (B) formed sequentially on the surface of a photosensitive drum are transferred so as to be overlaid one over another on a first surface (front surface) of a sheet supported on a sheet carrying member such as a transfer drum, transfer belt or the like, and thereafter said sheet is separated from said sheet carrying member and transported to a fixing device for fixing. Then, the aforesaid sheet is fed again so as to be supported on said sheet carrying member with a second surface (back surface) disposed as a transfer surface, and when said sheet arrives at a transfer position, toner images of four colors are sequentially transferred thereto so as to be superimposed one over another on said second surface in the same manner as the first surface, and subsequently said sheet is separated from said sheet carrying member and transported to a fixing device which fuses the overlaid toner image thereon, whereupon said sheet is ejected from the apparatus.
Image forming apparatuses of the electrophotographic type provided with a duplex printing function such as the above described apparatuses readily produce impaired stability during sheet transport due to trouble such as paper jams and the like.